Ok, I'm pretty sure you can post a journal after reading the rules of Other Writing, however, you have to think about this:
How regularly will you update it
If it will be something you just post here and there sometimes whenever you feel like it, then I would reccommend posting in the Daily Chit-Chat as Angela (and other posters) have suggested. If it's more serious (like daily) and written with structure (like a dairy) then I would reccommend making your own thread in the Other Writing.
How long each post will be
Again, If you will post only a paragraph or less, then you can just post it in the Daily Chit-Chat
How organised you need it to be
If you only want to let loose your feelings about the day and what happened; I suggest making your own thread in Other Writing.
If you need complete organisation (i.e. no posts between your entries), you can make a blogger/livejournal account and blog there everyday and post a link to it in your signature.
Astinus: I'm sorry if this is the wrong advice on posting in your forum, but it is titled Other Writing, not Other Fanfiction, therefore I'm assuming this is allowed.